Suramin, long known as an effective anti-microbial drug, has recently attracted much attention as a novel anti-tumor agent. This compound is particularly interesting because it seems to act by a variety of mechanisms and can affect a number of enzyme systems. In spite of the significant interest in suramin, no systematic study has been carried out on structure-activity relationships of suramin analogues. In looking at the suramin structure, it is clear that there are a number of opportunities for isosteric replacements. One particular change would involve replacing the carbonyl oxygens of suramin by thiocarbonyl groups. Changes in the substitution patterns of the sulfonate groups would also be investigated. Synthetic compounds would be tested in the National Cancer Institute's multi-cell line screen for anti-tumor activity. Students would be involved both in the design and synthesis of novel anti-tumor agents. This will provide a useful introduction to understanding how NCI and the pharmaceutical industry design novel therapeutic agents.